The present invention relates to generators, e.g., hydrogen cooled generators, and particularly relates to a flexible magnetic brush seal useful in various sealing environments in the generator. Particularly, the present invention relates to a hydrogen cooled generator employing a flexible magnetic rubber brush seal, e.g., as a low flow fluid film seal and/or as a diffusion and mass transfer prevention seal.
In turbomachinery such as gas and steam turbines, compressors and turbopumps, a number of seals are used at different locations for minimizing leakage flows. For example, seals may be provided between sealing surfaces which are both movable relative to one another or between components in which one component moves relative to another component, e.g., a housing wall and a rotating shaft.
Brush seals, particularly in turbomachinery, typically comprise a plurality of elongated wire bristles in contact with a movable, for example, rotating surface. The bristles provide a tight, rub-tolerant seal which experience only slight degradation over time. The bristles of the seal are compliant in use and thus minimize damage due to transient impact between the components being sealed. A typical brush seal is formed by folding bristles over a rod with an outer clamp maintaining the folded bristles, squeezing the bristles between a folded metal plate forming a clamp or sandwiching the bristles between a pair of supporting metal plates and welding the plates and bristles at their proximal ends to one another. The distal ends of the bristles typically project a certain distance from the margins of the backing plates or clamps to engage the opposing sealing component, for example, a rotor. Common to these types of brush seals is that the bristle holder or carrier is formed of metal which is usually machined with a tight tolerance and thus the brush seal is applicable only to specific sealing dimensions. For other sealing dimensions, for example, diameters, a separately manufactured and distinct brush seal must be used in order to dimensionally fit the seal with its carrier. Consequently, the brush seals are costly in terms of tooling, manufacturing and installation and long cycle times in brush seal manufacturing and retrofitting are required.
In generators, for example, hydrogen cooled generators, an end wall or casing surrounds a rotor and seals are interposed between the housing wall and the rotor to seal between a hydrogen atmosphere on one side of the wall and oil on the opposite side of the housing wall in a bearing cavity. Low flow fluid film seals are conventionally used on hydrogen cooled generators as dynamic rotor seals with near zero leakage. Turbine oil is the traditional working fluid of these seals because the turbine/generator unit must be supplied with turbine oil for its bearings. Low flow fluid film seals are generally directed along the rotor by a pair of low clearance rings about the rotor shaft. In a typical system, the oil flows past one seal ring into the bearing cavity and past the other seal ring and an additional oil deflection seal into the hydrogen environment within the housing wall. Oil entering the hydrogen side entrains hydrogen gas, which is then removed from the generator and vented from the system. Hydrogen consumption therefore represents a continuous and substantial expense to the user of the hydrogen cooled generator. The low flow fluid film seals and the oil deflection seals are typically about different diameters of the rotor.
In accordance with a preferred embodiment of the present invention, there is provided a brush seal for use in a generator at various and different sealing locations. For example, in a hydrogen cooled generator, the brush seal hereof may be used as a low flow film seal and/or as a diffusion and mass transfer prevention seal. The seal of the present invention comprises a brush seal having a seal body formed of a flexible magnetic material such as magnetic silicone rubber material. Preferably, the bristles are embedded, glued or otherwise secured to the brush seal body such that the bristles project from the body, terminating in tips for sealing engagement with the opposing sealing component such as the generator rotor. The bristles are preferably formed of Kevlar(copyright) or polyester material. It will be appreciated that by bending the magnetic silicone rubber of the brush seal body, the brush seal can fit a wide range of sealing dimensions, e.g., diameters, in complex sealing geometry. For example, where the brush seal is to be applied between a fixed annular structure and a shaft rotating within the annulus, the brush seal may be flexed to conform to the dimensions of the two components. It will be appreciated that the brush seal body, together with the bristles carried thereby, can be flexed or bent into virtually any shape, e.g., an irregular or circular shape having different dimensions and thus may be used as a brush seal for differently dimensioned components, such as low flow fluid seals and/or diffusion and mass transfer prevention seals used in hydrogen cooled generators.
Additionally, by forming the brush seal body from a magnetic material, the seal can be readily adhered to one of the sealing components. Preferably, the adherence is temporary until the seal body can be adjusted and secured in final position. Ancillary jigs or fixtures useful to maintain the brush seal body in position while adjustments are being made prior to final securement are entirely eliminated. The magnetic rubber is preferably formed of a composite material of ferrite magnetic powder and a silicone polymer. With these characteristics, the brush seal body can be bent, twisted or coiled and thus easily configured for installation.
In accordance with a preferred embodiment of the present invention, the flexible magnetic brush seal can be used as a low flow fluid film seal in the hydrogen cooled generator which reduces the film flow of oil into the hydrogen atmosphere, thereby reducing hydrogen consumption, with the added benefits of facilitating manufacture and assembly of the brush seal. To accomplish this, the flexible magnetic low flow film seal is provided between the rotor and the housing wall, segregating the hydrogen atmosphere on one side of the wall and the oil and air mix of the bearing cavity on the opposite side of the wall. The flexible magnetic brush seals may be provided in pairs with a coil spring engaging between the pairs of brush seal bodies, biasing the bodies for axial separation and radial inward movement toward the rotor to maintain the bristles in contact with the rotor. In this sealing environment, oil or another fluid for forming the fluid film is pumped into the sealing space at a higher pressure than the seal casing. The oil or fluid is constricted by the brush seal to create a low flow film seal. By reducing the flow of the fluid to a minimum required to maintain a complete circumferential film, hydrogen consumption is reduced.
The flexible magnetic brush seal may also be employed as a diffusion and mass transfer prevention seal in a hydrogen cooled generator. Thus, the brush seal hereof may be interposed as an oil deflector seal between the hydrogen atmosphere on one side of a generator housing wall and a seal cavity on an opposite side of the oil deflector seal. The seal cavity is an intermediate cavity containing lower purity hydrogen than the hydrogen-filled generator casing and generally lies inboard of the low flow fluid film seal. Typically, this seal is employed at an axial location of the rotor having a different diameter than the rotor diameter at the location of the low flow fluid film seal. Thus, a larger diameter flexible magnetic brush seal hereof is provided across the seal casing and rotor between the hydrogen cooled generator cavity and the seal cavity. This seal cavity greatly reduces the flow of hydrogen from the generator cavity across the seal into the hydrogen seal cavity and flow of oil along the shaft into the generator housing. As a consequence, a significantly greater difference between the purity of hydrogen of the two cavities on opposite sides of the seal casing is provided, affording reduced diffusion and mass transfer of the hydrogen across the seal. The brush seal in this sealing environment is also bi-directional, i.e., not only preventing diffusion and mass transfer of hydrogen into the seal cavity but also serving to prevent oil or oil mist from the seal cavity from entering the generator cavity.
Significantly, while the diameters of the two brush seals described for use in the hydrogen cooled generator are different, the same stock brush seal can be used for both seals. That is, a linear brush seal can be fabricated and, when cut to appropriate length, used as either seal. The brush seal is therefore not limited to a fixed diameter but is useful for a large number of different seal diameters.
In a preferred embodiment according to the present invention, there is provided in a hydrogen cooled generator having a rotor, a component part and a seal sealing between the rotor and the component part for segregating an at least in part hydrogen atmosphere on one side of the seal and a cavity on an opposite side thereof, the seal including a brush seal extending between the component part and the rotor, the brush seal including a brush seal body and a plurality of bristles projecting from the body with tips thereof engaging the rotor, the brush seal body being formed of a flexible material.
In a further preferred embodiment according to the present invention, there is provided in a hydrogen cooled generator having a rotor and a seal sealing between the rotor and a housing wall for segregating a hydrogen atmosphere on one side of the seal and a seal cavity on an opposite side thereof containing a gas of lesser purity than the hydrogen atmosphere, the seal including a brush seal extending between the component part and the rotor, the brush seal including a brush seal body and a plurality of bristles projecting from the body with tips thereof engaging the rotor and preventing diffusion and mass transfer of the hydrogen atmosphere on one side of the wall into the seal cavity, the brush seal body being formed of a flexible magnetic material.
In a still further preferred embodiment according to the present invention, there is provided in a hydrogen cooled generator having a rotor and a seal sealing between the rotor and a housing wall with at least in part a hydrogen atmosphere on one side of the seal and a bearing cavity containing a fluid on an opposite side thereof, the seal including a low flow fluid film brush seal extending between the wall and the rotor, the brush seal including a brush seal body and a plurality of bristles projecting from the body with tips thereof engaging the rotor for substantially segregating the hydrogen atmosphere and the fluid in the bearing cavity, the brush seal body being formed of a flexible magnetic material.